Hello! I have pasted an org-mode file with my question, it's
easies to explain by copying the below file and exporting it
to HTML.
Thanks,
--Erik
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* Silent code block evaluation on export.
The goal is to /run/ a code block on export for some side effect,
without any evidence in the exported file that this happened. For
example, loading some R package, reading in a dataset, or setting R
options. All this is presumably done with :session in mind, even
though I don't use it here.
In Sweave, we can specify the code block options echo = FALSE, results
= hide to faciliate this.
However, there are no command line arguments alone in org-mode that
can replicate such behavior. Below are several examples and how they
fail. There is also an example of a 'trick' that does work to
generate the output (or lack thereof) that we want.
/:results value/ tries to coerce its return value to a data.frame, so when
I reference 'non-conformable object' below, I mean something for which
the as.data.frame function generates an error.
* /:results value/ (the default for code blocks)
** with a simple object on the last line, a vector
This prints the return object, OK.
/:exports results :results value/
#+begin_src R :exports results :results value
2 + 2
#+end_src
** with a non-conformable object as the final value
This produces an error, as expected, and no output is produced, but
only by accident.
/:exports results :results value/
#+begin_src R :exports results :results value
summary(lm(1 ~ 1))
#+end_src
** using NULL as the last line
This does what we want, but requires a 'trick'. OK.
/:exports results :results value/
#+begin_src R :exports results :results value
summary(lm(1 ~ 1))
NULL
#+end_src
* /:results silent/
** with a simple object on the last line, a vector
This still prints the return object, it may be debateable if it
should. The combination of /:exports results/ and
/:results silent/ does not seem inherently self-contradictory.
/:exports results :results silent/
#+begin_src R :exports results :results silent
2 + 2
#+end_src
** with a non-conformable object as the final value
However, with a non-conformable object on last line, an error is
produced when the code is evaluated in the buffer. I'm wondering if
/:results silent/ is specified, why the cast to data.frame is
occurring? It could be happening for good reason that I'm not aware
of. The lack of output here is due to an error occurring.
/:exports results :results silent/
#+begin_src R :exports results :results silent
summary(lm(1 ~ 1))
#+end_src
** using NULL as the last line
This does as we want, using the NULL trick.
/:exports results :results silent/
#+begin_src R :exports results :results silent
summary(lm(1 ~ 1))
NULL
#+end_src
* Ideas
Since the NULL trick is R-only, how could we specify command line
options to faciliate this use case?
Possible solutions:
0) There already exists a solution that I don't list here.
1) Make /:exports results :results silent/ do it, but note the results
above with a non-conformable object!
2) Make /:exports none/ still evaluate the code block on
export. Probably counter-intuitive.
3) Make export use the /:eval/ argument combined with /:exports/,
maybe something like: /:exports none :eval yes/
4) Another better solution!
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